<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>后盾人</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        article {
            border: solid 10px blueviolet;
            width: 400px;
            height: 400px;
            margin: 100px;
            position: relative;
        }

        section {
            position: relative;
            background: #ddd;
            width: 100%;
            height: 100%;
            left: 100px;
            top: 300px;
        }

        div {
            background: blueviolet;
            width: 200px;
            height: 200px;
            left: 50%;
            top: 50%;
            margin-left: -100px;
            margin-top: -100px;
            position: absolute;
        }
    </style>
</head>

<body>
    <article>
        <section>
            <div></div>
        </section>
        <div></div>
    </article>
</body>

</html>